1. Field of the Invention
The present invention relates to a semiconductor memory device that, besides storing data in memory cells, also stores and can output identifying information and repair information.
2. Description of the Related Art
For a variety of purposes, including testing purposes, semiconductor memory manufacturers find it useful to store identifying information in memory devices. In one conventional scheme, the identifying information is stored by blowing selected fuses in a so-called fuse box in the device, and is read out when a clock signal and an enable signal are supplied. Japanese Patent Application Publication No. 11-121566 shows one example of this scheme, implemented using a counter. A different conventional example, also using a counter, will be given in the detailed description of the present invention.
To increase production yields, the memory cell arrays of large-scale memory devices include redundant memory cells that can be used to replace defective memory cells. Repair information identifying the memory cells that have been replaced, needed to direct access to the redundant memory cells that replace them, may also be stored in a fuse box. Japanese Patent Application Publication No. 05-047196 shows one example of this scheme; another example will be given in the detailed description below.
External output of the information identifying replaced memory cells is useful during the testing of memory devices. In a roll call test, for example, a sequence of address signals is supplied to the memory device, which outputs a bit of information indicating whether each addressed memory cell, or group of memory cells, has been replaced. A roll call enable signal is used to enable the output of this information, instead of output of the data stored in the memory cells.
It would be desirable for a memory device to be capable of output of both identifying information and roll call information, but if the conventional schemes outlined above are combined in a straightforward way, the necessary circuitry takes up excessive space. In particular, the two fuse boxes take up considerable space. The counter used for output of identifying information also takes up space.